JPS58115742A - Ion source unit in mass spectroscope equipment - Google Patents

Abstract

PURPOSE:To increase ion irradiation effect and improve detecting sensitivity by applying a voltage between both the front and rear ends of an ion source box and forming an electric field in the ion source box so as to accelerate an ion toward an exit hole. CONSTITUTION:An ion source box consists of stainless steel flanges 11 and 12 and a cylinder 10 with a conical hollow section 2, and several volts DC voltage is applied between both these flanges 11 and 12. The cylinder 10 is made of a semiconductor, constant current is applied thereon by voltage impression and a distribution of a equipotential surface indicated by dotted lines is obtained at the conical hollow section. A generated ion advances while converging in the direction vertical to the equipotential surface, i.e. toward an ion exit hole B due to this electric field. Besides, extraction effect can be improved by setting also the position of a thermo-filament 3 acting as an electronic source on the center axis.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion source device in a mass spectrometer, and aims to improve ion extraction efficiency.

Chemical ionization
(abbreviated as C), a reagent gas such as methane, isobutane, ammonia, etc. is constantly flowed into the ion source, and the reagent gas molecules are ionized by electron impact ionization and ion molecule reaction while maintaining the pressure inside the ion source at approximately I Torr. to generate reactive ions. The sample is introduced into the ion source in this state, and the sample molecules are ionized by the ion-molecule reaction between the reactant ions and the sample molecules.This method has the advantage of easily obtaining information on the molecular weight of the sample, and is widely used.

FIG. 1 shows a schematic diagram of a conventional chemical ionization ion source and a part of an analysis section.

A reagent gas is flowed from the gas supply pipe 1 to the ion source box 2, and the pressure inside the box is maintained at about I Torr. The box is provided with an electron entrance hole A and an ion exit hole B. Thermionic electrons emitted from the pock on the axis of the electron entrance hole A are accelerated to several tens of eV to several hundreds of eV and are made to enter the box to ionize reagent gas molecules. Furthermore, reactive ions are generated by an ionic-molecule reaction between the generated ions and reagent gas molecules.

When a sample is introduced here, the sample molecules are ionized due to the ion-molecule reaction between the reactive ions and the sample molecules.The generated sample ions are extracted from the ion exit hole B, and the sample molecules are ionized through the ion exit hole B. C and enters the analysis section 7. 4, the ion extraction electrode 25 is a converging lens electrode.

In order to ensure the practical life of the wall filament 3, the area outside the ion source box should have a vacuum better than 10 Torr. The analysis section is ↓OT to obtain good mass separation characteristics.
Make the degree of vacuum better than orr.

For this reason, the ion source section and the analysis section are vacuum isolated by a partition wall 6, and are evacuated by vacuum pumps 8 and 9 independently.

Inside the ion source box (~I Torr ), outside ((10
In order to maintain a pressure difference of -'Torr), the ion source is required to be highly airtight. Therefore, both the electron entrance hole and the ion exit hole have to be small holes. Generally, the conductance of the ion source box is 1 to 5'.
xlot t/F3 or so is in practical use.

Since the ion source box has a highly airtight structure, there are the following problems. An ion extraction electrode is installed after the ion exit hole, but the ion exit hole restricts the penetration of the extraction electric field created by this electrode into the ion source box, resulting in a low extraction efficiency for generated ions. This is one of the limiting factors for the sensitivity of mass spectrometers. Furthermore, since the internal pressure of the ion source box is as high as I Torr, ionization by electrons of several tens of eV to several hundreds of eV is limited to the vicinity of the electron entrance hole, which is also a limiting factor for extraction efficiency.

The present invention solves this problem and provides a highly sensitive mass spectrometer by improving ion extraction efficiency. That is, a voltage is applied between the front and rear walls of the ion source box to form an ion accelerating electric field within the box from the rear wall to the center of the front wall, and the ions generated within the box are directed to the ion exit hole. It consists of a cylinder 10 holding an extruded ion source box. Flange 11,1
2 is made of stainless steel, and a DC voltage of several square meters is applied between both flanges. The cylinder 1o is made of a semiconductor material, and when a voltage is applied, a constant current flows, and an equipotential surface distribution shown by dotted lines in the figure is obtained in the conical hollow region. The generated ions travel in a direction perpendicular to the equipotential surface, that is, toward the ion exit hole B, while being focused by this electric field. In other words, all ions generated at any point within the ion source box gather at the ion exit hole and are extracted.

By locating the hot filament 3 as an electron source on the central axis, extraction efficiency can be improved.

The cylinder 10 has a glass surface coated with a semiconductor. It is possible to use a method such as using ferrite, or to use zinc titanate ceramic or barium titanate ceramic, which are practically used as continuous dynode electron multiplier tubes. Especially 3
This semiconductor ceramic is excellent for use up to about 00°C.

It is also easy to extract positive and negative ions by switching the polarity of the DC voltage applied between the flanges 11 and 12. Although it is effective to apply the present invention to a C ion source, it can also be applied to an electron impact ion source, so it can also be used to configure an ion source for both electron impact ionization and chemical ionization.

FIG. 3 shows another embodiment of the present invention, in which the peripheral side wall 10 of the ion source box is formed of an insulator, and the front wall 12 and the rear wall 1 are
1 is a conductor, and the front wall 12 has a smaller area than the rear wall 11, so that the equipotential surface inside the box is shaped close to a concentric spherical surface. By making the rear wall 11 a concave spherical surface as shown, a more desirable electric field can be formed. Other parts corresponding to those in FIG. 2 are given the same reference numerals.

Note that in this embodiment as well, the side wall 1o may be formed of a high-resistance material.

The ion source device of the present invention has the above-described configuration and forms an electric field in the ion source box that accelerates ions toward the ion exit hole, so the ion exit effect is high and the detection sensitivity is increased. This is highly effective in a C ion source device in which the ion exit hole must be made smaller because it is necessary to maintain a higher gas pressure inside than the outside.

[Brief explanation of drawings]

FIG. 1 is a schematic longitudinal sectional view of a conventional example, and FIGS. 2 and 3 are longitudinal sectional side views of different embodiments that have not yet been invented. DESCRIPTION OF SYMBOLS 10... Circumferential side wall of the ion source box, 11... Flange forming the rear wall of the ion source box, 12... Flange forming the front wall of the ion source box, A... Electron incidence hole, B... - Ion exit hole, 3... filament. Agent Patent Attorney Kosuke

Claims (2)

[Claims] (1) The peripheral side wall of the ion source box is made of an electrical resistor or an insulator, and a voltage is applied between the front wall and the rear wall of the box, and ions directed toward the ion exit hole are generated inside the box. An ion source in a mass spectrometer characterized by forming a focused electric field. (2) An ion source device in a mass spectrometer according to claim 1, wherein the electron entrance hole is provided on the same axis as the ion exit hole in the rear wall of the ion source box.